Rotors for OTA: Channel Master, Nexxtech/Archer, Yaesu, Hy-Gain, Others

[300sflyer]

For whatever it's worth, both the new motor and the older one are reading about 8 ohms across any 2 connectors.

[iblackford]

That seams to answer it then, I'd say if the winding resistance is the same, than you are safe to put 30V to the 18V motor.

Remember, if you're using the digital controller, the 5V regulator may need extra heatsinking to handle the increased supply voltage. From the circuit that I saw, the rest of the circuit should be able to handle the increased voltage.

Ivan

[wilspin]

Well fuctionality of my CM rotor returned with the warmer weather -2c.

[majortom]

The rotor here is drawing 790 mA AC from the #1 Terminal of the CM 9510A controller (30 VAC), Outside Temp 29 deg F. For kicks, wait for a really cold morning (Tue,Wed,Thur from forecast), and see what it draws. Might be interesting to compare to someone's 18 V unit that's freezin up...

[wilspin]

In theory the slower the motor turns the more it will draw. Any time as motor is prevented for spinning at rated rpm it draws more. Like peak loads during start up. So I’ll bet I know what the test result will be.

[majortom]

yeap, the point of the test would be to see if that the little wallwart power supply that comes with the newer ones just doesn't have enough "onions" to drive the motor when it's cold out. Got a multimeter there?
Edit: 795 mA AC from the same terminal, 12 deg F.

[wilspin]

Of course MT, it’s not a voltage issue but an amperage available issue! The test should be how much does the voltage drop during start up on either set up 18 or 30. What would be acceptable 20% 30%? Higher voltage used (30) on an 18 v unit will compensate a bit for the drop. Once the motor is at speed the voltage will be too much. The real solution may be 18v power supply with higher available output (onions) say 2A instead of 1.

[wire_in_the_sky]

We seem to be converging on the root cause. A Power supply with insufficient current capability to start the motor at low temperatures. One way to test this hypothesis would be to parallel the outputs of two identical power supplies and see if it overcomes the freezing issue. If you try this, make sure that you get the polarities right. Otherwise, you risk burning out both power supplies.

A partial solution would be to go to a larger wire, especially for long runs, to reduce the resistance of the control wire and make more of the scarce power supply current available for the motor.

If the capability of the power supply is indeed the problem, how do we get Channel Master to fix it? And what about complaining to the retailer? Does Save'N Replay know about this? They sold me my unit.

Does anyone have two identical 18V power supplies that they could parallel to test this out. It is a heck of a lot safer for the motor than exposing it to a voltage of 1.7 times the motor rating (30 V on a 18 V motor). High voltage would work for a limited period of time but would damage (destroy?) the motor over time. And a rotor motor that is 50 feet up in the air is not readily replaced.

[majortom]

I don't have a frozen one to test with, but some basic math tells the story.

The old one I have, is capable of 30 VAC @ 1 A or 30 VA (~ 30 Watts if we ignore power factor for a moment). Compared to the new one u guys have, 18 VAC @ 1A or 18 VA (~ 18 watts).

The temperature issue is two fold the way I see it.
a.) Any motor large or small will have less efficiency at cold temperatures compared to their efficiency at Normal Operating temperatures.
b.) The mech. drag is increased in the cold (from the Grease, etc.)

Small AC motors have very low efficiency to begin with, relative to say a motor used in ur washing machine or sumthin. Power consumption just isn't normally a design constraint for a small motor. So neither is efficiency.
If it were me, I would just try and find something middle of the road, that used a larger wall wart, like from an old DSL Modem or sumthin, that ran on 24 VAC / 1A for ~24 watts and put the proper connector on the end, and try that to see if it helped.
And as someone else already mentioned, I'd probly be more concerned with the increased power dissipation of any internal voltage regulator of the control box itself, than hurting the motor. If ya used a higher voltage in to the control Box, Power Dissipated by any Voltage regulator is (Vin - Vout) x Load Current, since Vin ^^^ so would the Pwr dissipated by the regulator. That's why I'd say meet it half way for a quick test...

[iblackford]

Originally Posted by wire_in_the_sky

We seem to be converging on the root cause. A Power supply with insufficient current capability to start the motor at low temperatures. One way to test this hypothesis would be to parallel the outputs of two identical power supplies and see if it overcomes the freezing issue. If you try this, make sure that you get the polarities right. Otherwise, you risk burning out both power supplies.

A partial solution would be to go to a larger wire, especially for long runs, to reduce the resistance of the control wire and make more of the scarce power supply current available for the motor.

If the capability of the power supply is indeed the problem, how do we get Channel Master to fix it? And what about complaining to the retailer? Does Save'N Replay know about this? They sold me my unit.

Does anyone have two identical 18V power supplies that they could parallel to test this out. It is a heck of a lot safer for the motor than exposing it to a voltage of 1.7 times the motor rating (30 V on a 18 V motor). High voltage would work for a limited period of time but would damage (destroy?) the motor over time. And a rotor motor that is 50 feet up in the air is not readily replaced.

Putting 30V on an 18V motor isn't necessarily a problem, in fact, we don't know the maximum current the motor can handle. All we know is that some control boxes output 30VAC, while others output 18VAC. 300sflyer's resistance measurements of the coils suggest that the motors are largely similar.

If you're still concerned, what can be done is to put a pot in series with the motor coils, one for each coil, and a 30V control box or transformer used. The pots can be adjusted, slowly incrementing the current going to the coils until the motor moves in cold weather. The pots must be high wattage, enough to handle the full current that the motors will see.

I'd agree with the larger conductor wire though, when I put up a 80' tower just over a year ago, I used 16ga extension cord wire. It works well, never freezing up in the winter.
I believe it was a 30VAC control box.

[hoopitup2000]

Originally Posted by iblackford

I'd agree with the larger conductor wire though. . . .

I agree. Replaced the Channel Master 22 gauge wire (80 feet) with Radio Shack 20 gauge wire & my reliability issues disappeared. Can't compare the temperatures we get here with those in Canada, but the unit works fine down to at least 10°F here.

[wilspin]

Major T is right you just can pump more juice thru the control unit. Direct feed to the motor for testing?

[roger1818]

Originally Posted by iblackford

This torque can be increased by increasing the drive voltage. The only limitation to this is that the motor windings use a certain conductor size, which limits how much current that they can safely handle.

It is actually the current through the windings that affects the torque (the strength of the magnetic field is proportional to the current through the winding). While Ohms law states that voltage and current are proportional, there is a voltage drop in the wires between the controller and the rotor. As a result it would be optimal for the controller to have a constant current source, but it is likely that most have a constant voltage source since it is cheaper and easier.

[iblackford]

Indeed, torque is proportional to current, however given the fixed resistance of the motor and the installed wires, the drive voltage must be increased.

A constant current source will achieve the same result: voltage at the terminals of the motor will be higher. The constant current source, with enough voltage headroom, will just give you a constant current regardless of the load resistance.

Ivan

[300sflyer]

My CM rotor is still working just fine. The increase from 18V to 30V using the older CM contoller, has had no ill effects thus far.